This page contains answers to Seagull CES test about Fuel Combustion Efficiency, and serve as a database of questions and answers, using which seafarer can prepare to exams for getting certificate of competence, or just to challenge yourself with knowledge in this theme.
CBT CD 0047 – Fuel Combustion Efficiency.pdf
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Amount of questions: 19.
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A large increase in cylinder pressure occurs:
When there is a small delay between beginning of injection and actual ignition.
When there is a large delay between beginning of injection and actual ignition.
When there is no delay between beginning of injection and actual ignition.
A too late combustion leads to:
Decreased exhaust gas temperature.
No change in exhaust gas temperature.
Reduced soot information and cleaner turbo chargers.
Increased exhaust gas temperature.
Fuel must be atomized and distributed finely through the combustion chamber:
To increase the pumping volume.
To increase the surface area available for ignition.
To prevent fuel accumulation.
How will a large content of “Cat fines” in the fuel influence the injection timing?
Cat fines will improve the fuel quality and lead to early injection.
Cat fines will have no influence on the injection and combustion.
Cat fines will improve the atomisation and thus the combustion.
Abrasive wear of pumps and valves will lead to late injection.
The combustion process starts when:
The fuel pump starts working.
The exhaust valve is closed.
When there is an increase in cylinder pressure.
The cylinder liner temperature is lower than normal when:
You have an early injection of fuel.
You have a late injection of fuel.
You have a poor atomisation of the fuel.
Increased RPM.
The maximum cylinder pressure will be higher than normal when:
You have an early injection of fuel.
You have a late injection of fuel.
The fuel valve opening pressure is too high.
You have a leaking fuel valve.
The maximum cylinder pressure will be lower than normal when:
You have an early injection of fuel.
You have a late injection of fuel.
The mean indicated pressure is higher than normal.
The cylinder liner temperature is below normal.
The opening of the exhaust valve in MAN B&W MC engines is by:
Air spring pressure.
Fuel Oil pressure.
Hydraulic oil pressure.
The purpose of VIT is:
To optimize fuel economy at part load.
To optimize fuel economy at full load.
To reduce wear on fuel pumps.
The purpose of suction valve is:
To permit inlet to fuel pump.
To avoid additional opening of injection valves.
To prevent sticking of fuel pump plunger.
What do we mean by the expression after burning?
The fuel valves are leaking and the combustion continue.
Some fuel will continue to burn until the exhaust gas has passed the exhaust boiler.
The fuel is ignited twice to obtain a more clean combustion.
When the combustion continues after the injection has ended.
What do we mean by the fuels cetane number?
The cetane number is related to the combustion temperature.
The cetane number is related to the ignition quality of the fuel.
The cetane number is related to the pump index.
The cetane number is related to the cylinder oil.
What is controlled combustion?
Vaporising and reaction with oxygen is executed at the same rate as injection.
Using the VIT system continuously during combustion.
Changing pump index according to fuel quality.
Checking the exhaust gas for possible soot content.
What is the advantage of using three injection valves on each cylinder?
You can inject more fuel to each cylinder.
You will have longer maintenance intervals and lower cost.
A more uniform temperature distribution around the combustion space.
Each injection is smaller and easier to handle.
What is the approximate opening pressure for the fuel injection valves on a MAN B&W MC90 engine?
420 bar.
500 bar.
350 bar.
480 bar.
What is the effect of high viscosity on after burning?
The after burning will be reduced due to better atomisation of fuel.
Viscosity has no effect on after burning.
The after burning will last longer due to increased droplet size.
Fuel pump capacity will be reduced and give less after burning.
When the fuel injector is closing a pressure wave will start travelling in the fuel pipes at a velocity in order of 1 300-1 500 m/s. If this is continuing, what problem will it cause?
The fuel pump will supply a variable amount of fuel to the injector.
The fuel pump suction valve will start leaking.
The fuel pipes will be damaged and start leaking.
The fuel injectors will normally start dripping.
You have received a fuel with poor ignition quality, which of the following would you do?
Collective adjustment towards more late injection.
Change the Pump index.
Collective adjustment towards more early injection.
Mix the fuel with additives.
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